The Study Of Durability And Embankment Reinforced On Soft Soils By Geotextiles

The paper expounds the development history of geosynthetics as well as the types of geosynthetics used in port works and the scope of application of geosynthetics. The internal factors affecting the geosynthetics such as the types of materials used, physical structure and additives used as well as the influence of ultraviolet rays, temperature, chemical organism, climate and mechanical wear upon the durability and ageing resistance of geosynthetics are analyzed briefly. Durability of geotextiles and present research and study of geotextiles are also analyzed.Based on the field sampling and tests of the geotextiles used in the pilot dams for the works training the waterways of the Changjiang River at Jiepai and the Hanjiang River as well as the available data and results of tests made both at home and abroad, the influence of different purposes of usage, different materials and different textures of geotextiles upon the durability of geotextiles is analyzed and by so doing the durable life of geotextiles commonly used on engineering projects is given.With the measured data of the dissipation of pore water pressure of the geotextile-reinforced course, settlement of foundation, tensile stress of geotextiles and pressure on the embankment of the breakwater for Huanghua Port, the magnitude and characteristics of the distribution of tensile stress of the geotextile-reinforced course and their relationship with the settlement of the foundation below the breakwater are analyzed. The measured data showed that the pressure distribution on the foundation soil tended to homogenize and the tensile stress developed was lower than the design tension force, thus raising a new problem in considering the magnitude of tensile stress when the stability of a synthetic-reinforced course is being analyzed.In combination with the construction of the breakwater for Huanghua Port and on the basis of the tests of the centrifugal models of bedding courses with and without reinforcing geotextiles and with different types of geotextiles, the displacement field of particle movement of foundation soil, process of development of pore water pressure, settlement or uplift of foundation surface and the tensile force of geotextiles at the axial symmetric point of the breakwater were analyzed. The ultimate height of the breakwater was discussed in accordance with the test results and the deformation characteristics and stability of the foundation under different working conditions werealso studied. The reinforcing mechanism of geotextiles and the stability of the geotextile-reinforced foundation were also analyzed and discussed. It can be concluded from the field and laboratory centrifugal model tests that,(1) By altering the distribution of the consolidation stress in the breakwater - bedding course– foundation system and the distribution of the shear stress of the foundation surface, the geotextiles-reinforced bedding course may restrain the uneven settlement of a foundation and reduce the lateral displacement and can also improve the stability of breakwaters and dams, thus increasing the ultimate bearing capacity of foundations.(2) The reinforcing effect of geotextiles may be affected by a number of factors like the width of laid geotextiles, strength and modulus of the geotextiles and interfacial strength. Generally, the wider the geotextiles is laid and the higher the strength of geotextiles is, the better the reinforcing effect of the geotextiles will be. To ensure the full play of the reinforcing effect of geotextiles, the strength and modulus of the textile should match the interfacial strength of the sand cushion.The load borne by the geotextile-reinforced bedding course is mainly the internal load generated by the body of the breakwater itself. Assuming that the internal load generated by the body of a breakwater itself is partially borne by the geotextile-reinforced bedding course (with a proportion of bearing ofηt) and partially borne by the foundation, an analytical equation is derived for the stability of a foundation with a geotextile-reinforced bedding course on the basis of the theory of ultimate equilibrium. The calculations thus made indicate that the simple slice method for circular slip surface and the logarithmic spiral surface method presented in this paper may well reflect the anti-sliding effect of the geotextile-reinforced bedding course. The sliding resistance of a geotextile-reinforced bedding course and the position of sliding surface is related to the depth of the foundation. The anti-sliding resistance is significant when the sliding develops in shallow strata, but the anti-sliding effect is less remarkable when the sliding develops in deep strata.